This invention relates generally to lightweight, high-strength structural panels or laminates and more particularly, to faced polyurethane boardstock of a sandwich-type construction useful to provide desirable thermal insulating properties. Such panels are used on the inside of metal buildings; in inverted roof systems; in conventional built-up roofing; in residential sheathing, replacing plywood or fibreboard; and in the cavity walls of commercial buildings. Its primary function is one of permanent, lightweight, efficient insulation.
Structural panels or laminates are fabricated by bonding thin facings or skins of high tensile and compressive strength to lightweight core materials such as polyurethane foams. The bonded core material in the sandwich stabilizes and stiffens the thin facings, and in present-day interior construction, also frequently is made of a material having fire retardant properties. A variety of materials are presently used to provide facings or skins to cover rigid urethane foam insulation. The basic objectives of such a facing include good tensile strength and puncture resistance such that the facing acts both as a substrate in the foaming operation and as a protective coating during installation; low water vapor permeability value in order that high humidity does not reduce the insulation value of the foam; low flammability of the facing such that a faced board has a lower flamespread and fuel contribution than an unfaced board; good long-term adhesion between the facing and the foam so that the facing remains useful for the lifetime of the insulation; a low coefficient of linear expansion such that stress between the facing and the foam surface does not cause delamination or warpage; a reflective surface; rigidity for foam processing; negligible change in dimensions, up to 350.degree. F., etc. In prior construction panels, difficulty has been experienced in economically constructing the panels with the necessary structural rigidity for satisfactory service and simplified installation, while at the same time retaining all of the above-described desirable properties in the panel structure. The laminate and construction panel of this invention accomplish each of these objectives by using as the facing a metal foil, scrim, tie-coat combination not heretofore known.
Metal, e.g., aluminum, foil has been used heretofore as a facing in forming laminates used in panel construction. To have acceptable puncture resistance and have a low coefficient of linear expansion, it has heretofore been necessary to use heavy hard foil, e.g., 1 mil or 1.5 mil thick and 1/4 or 1/2 hard. These foils are heavy and hard to handle as they puncture and tear easily. While initial adhesion between the foil and a conventional urethane foam can be good, increasing use of highly chlorinated polyols in urethanes and the use of polyisocyanurate systems, both with their inherent friability, has led to the use of a tie-coat on the foil. Originally, a nitrocellulose lacquer was used but more recently urea-formaldehyde modified baking epoxies have been applied to provide a better bonding surface for the urethane foam.
Many attempts have been made to overcome the disadvantages of plain foil facings. Chiefly, these attempts have involved the addition of Kraft paper and, on occasion, a scrim. This type of facing can have acceptable puncture resistance and a low coefficient of expansion which varies glass &lt; paper &lt; foam &lt; foil. However, the flammability of the paper is a definite disadvantage together with the possibility of moisture "wicking" through the paper. Moisture will eventually cause delamination of the facing or degradation of the foam. Several fire retardant paper variations are on the market but their cost is considerably higher than the product of this invention. It is also known to make a construction panel from a urethane foam core continuously laminated to fiberglass reinforced aluminum skins to form a tough, uniform sandwich panel. Such prior art construction panels have substantial advantages over the earlier construction panels in that the urethane-fiberglass reinforced aluminum panels are lightweight, strong and rigid and dimensionally stable while providing high insulating efficiency, both thermal and acoustical. However, the problems relating to the weight and hardness of the foil have not been overcome and difficulties in providing a strong bond between the foil and foam, as well as the scrim, still exist.
The foil/scrim laminate of this invention overcomes these disadvantages in known constructions by use of a scrim to support the foil and by the adhesive tie-coat used to bond the foil and foam so that it reacts with the urethane foam during manufacture to chemically bond or weld to the foam. This invention permits use of substantially thinner, less hard foil and permits reduction in the weight of foil required by some 40 to 115% over the previous use of plain foil. Further, tensile and puncture are greatly improved, and the coefficient of linear expansion of the laminate is less than that of the foil due to the presence of the scrim. The foil/scrim laminate of this invention can be produced using the selected tie-coat material also as a laminating adhesive such that the machine-time to tie-coat the foil is the same as the machine-time used to laminate the scrim to foil.